Wafer temperature is known to be an important processing parameter in the manufacture of semiconductor devices. Wafer temperature variation can be both wafer-to-wafer (e.g. in a batch process) and across a given wafer, whether in a batch process or not. Temperature variation is known to introduce non-uniformities in processing parameters, such as etch rate, deposition rate, plasma density, grain growth, and doping levels, across a wafer. Such non-uniformities can reduce yield by resulting in widened distributions for devices formed even within a given die, such as for dimensions and parametric values like voltage thresholds and resistance values. There is thus a need to detect and monitor process temperature variation across wafers during processing to allow improved process control and for more robust process development. The method should be rapid, provide high spatial resolution, and not require expensive equipment.